1. The Institute for Advanced Studies Wuhan University Wuhan 430072 China
2. School of Electrical Engineering Wuhan University Wuhan Hubei 430072 China
3. College of Materials Science and Engineering Hunan University 410082 Changsha Hunan China
4. Department of Applied Chemistry National Yang Ming Chiao Tung University 1001 University Road Hsinchu 30010 Taiwan Republic of China
5. National Synchrotron Radiation Research Center Hsinchu 30076 Taiwan Republic of China
6. Key Laboratory of Artificial Micro and Nanostructures of Ministry of Education Hubei Key Laboratory of Nuclear Solid Physics School of Physics and Technology Wuhan University Wuhan 430072 China